The invention relates to an optoelectronic monitoring device comprising at least one transmitter arranged at an end of a monitored zone, at least one reflector arranged at an end of the monitored zone opposite the transmitter for electromagnetic radiation transmitted by the transmitter and at least one receiver for radiation reflected by the reflector. The invention further relates to a method of detecting objects intruding into a monitored zone.
Such monitoring devices and detection methods are generally known and serve to detect objects intruding into the monitored zone. The use of such monitoring devices takes place, for example, at hazardous machinery or at devices relevant to safety at which the intrusion of objects or persons, or individual body parts, into the monitored zone, also known as the protected zone, should be prevented. The monitoring device in this manner provides for the safety of the persons working on the machine or for the security of the monitored or protected zone.
It is an object of the invention to provide an optoelectronic monitoring device of the kind first named which, while functioning reliably, is as secure as possible against manipulation and is as insensitive as possible with respect to external interference radiation and which should in particular have a favorable cost and allow the detection of objects in the monitored zone with high resolution. Furthermore, an improved detection method should be provided.
This object is satisfied, on the one hand, in that the transmitter has a group of transmission elements which are spaced apart from one another and which each transmit electromagnetic radiation into the monitored zone. A receiver has at least one spatially resolving reception element for radiation reflected by the radiator and an evaluation device is provided which is coupled to the reception element. The transmitter, the reflector and the receiver are made and arranged such that, during the monitoring operation, at least one part of the group of transmission elements including a plurality of transmission elements is imaged on the reception element by means of the reflector so that a check can be made by means of the evaluation device as to whether a pattern on the reception element formed by the imaged transmission elements deviates from an expected image of the transmission elements.
In accordance with the invention, the transmission elements of the transmitter and the reception element of the receiver form an active side and the reflector at the end of the monitored zone opposite the transmission elements forms a passive side of the monitoring device. If the radiation transmitted by at least one transmission element is interrupted, e.g. by an object intruding into the monitored zone, then this infringement of the monitored zone, or protected zone, is recognized in that a deviation of the pattern detected on the reception element from the expected image of the transmission elements occurs by means of the evaluation device. In this connection, the resolution of the monitoring device, i.e. the detection limit, is defined by the distance of the transmission elements from one another. The resolution of the device can generally be increased as desired by the selection of a correspondingly low spacing between the transmission elements, which preferably lie in one plane and form radiation sources.
In accordance with the invention, only a single reception element is required for the group of transmission elements, i.e. it is not necessary to associate a receiver with every transmission element. A particularly cost favorable active/passive construction is thereby realized. Alternatively, in accordance with the invention, a plurality of reception elements can also be provided.
A further advantage of the monitoring device of the present invention consists of the fact that any displacement of the passive part, i.e. of the reflector, relative to the active part is recognized, since the pattern of the group of transmission elements detected on the reception element deviates from the expected image of the group of transmission elements with a relative arrangement between the transmitter, the reflector and the receiver not in accordance with their purpose. As a result, the monitoring device of the invention is highly secure against manipulation. A deflected reflection of the radiation transmitted by the transmission elements, e.g. by introducing additional beam deflection means into the beam path, carried out for purposes of manipulation, results in a spatial displacement of the imaged transmission elements on the reception element, which is recognized by comparing the actually detected pattern of the transmission elements with the expected pattern.
Further, the imaging of the transmission elements advantageously takes place in accordance with the invention such that interference radiation not originating from the transmission elements cannot impact in the regions of the reception elements in which the radiation transmitted by the transmission elements and reflected by the reflector is detected. As a result, the monitoring device of the invention is highly secure against interference radiation.
Respectively separate units are not necessarily to be understood as the transmission elements in the sense of the invention; the transmission elements can rather be radiation sources generally realized in any manner. The wavelength of the radiation used can generally be any wavelength in accordance with the invention and can lie both in the range visible to the human eye and in the range invisible to the human eye.
The radiation sensitive area of the reception element is preferably smaller, and in particular substantially smaller, than the area over which the transmission elements are distributed. The imaging of at least some of the transmission elements is preferably achieved by an optical imaging system of the receiver which is matched to the respective circumstances and which is interposed in front of the reception element, with the optical imaging system or the optical receiving system preferably having a multi-lens system.
In a preferred practical embodiment of the invention, provision is made that the receiver is arranged in the region of the transmitter and preferably in direct proximity to the transmitter. It is particularly preferred for the receiver and the transmitter to be combined to form one module. An advantageous modular construction is thereby made possible in which a plurality of modules including at least one respective transmitter and at least one receiver can be combined together to form a transmission/reception system. With such a modular system, low demands result in an advantageous manner on the number of transmission elements per module, which is required for monitoring security which is sufficient in accordance with the respective application, and on the opening angle of the modules.
In accordance with a further preferred embodiment of the invention, a single row arrangement of transmission elements is provided. A narrow construction of the active side of the monitoring device, which is advantageous for certain applications, can be achieved by this one-dimensional arrangement of the group of transmission elements. The receiver, or its reception element, is preferably arranged on a line with the row of transmission elements, but can also be positioned to the side of the transmission elements.
A two-dimensional arrangement of the transmission elements, and thus a three-dimensional monitored zone, is achieved in accordance with a further preferred embodiment in that a multi-row arrangement of the transmission elements is provided. In this connection, these elements preferably form lines and gaps extending perpendicular to one another. The transmission elements can also be arranged asymmetrically.
A further embodiment of the invention provides for at least one reception element to be provided on which the group of transmission elements is completely imaged. Precisely one such reception element is preferably provided. The number of individual components for the monitoring device in accordance with the invention is thereby minimal.
Alternatively, it is also possible in accordance with the invention for a plurality of reception elements to be provided which are spatially separated from one another. In this way, the monitored zone can generally be given any desired shape. For example, only part of the group of transmission elements can be respectively imaged on each reception element. It is, however, preferred for all transmission elements to be imaged on each reception element, whereby a particularly high monitoring security is achieved. Generally, a plurality of transmission elements can simultaneously be imaged on a plurality of reception elements.
In accordance with a further preferred practical embodiment of the invention, the reflector includes a mirror unit. In a particularly simple, and thus low price, embodiment, the mirror unit includes precisely one plane mirror.
The reflector can furthermore include a plurality of individual reflectors which are preferably each formed by a plane mirror.
An overlapping of individual regions of the monitored zone, which is advantageous for specific applications, can be achieved in accordance with a further preferred embodiment of the invention in that the reflector includes at least two individual reflectors tilted with respect to one another.
In accordance with a further preferred embodiment of the invention, the reflector is made as a retro-reflector or as a triple mirror or in the form of, for example, a roof-shaped reflector which acts as a retro-reflector or as a triple mirror at least with respect to a radiation propagation plane. The monitoring device of the invention is thereby given an advantageous tolerance with respect to inexact alignments; i.e. the angular availability of the monitoring region is increased since the incident radiation is reflected parallel to the direction of incidence irrespective of the angle of incidence.
In a particularly simple realization, the reflector can here include only two plane mirrors, which extend at right angles to one another, and in particular be made as a so-called roof-type reflector. A reduction in the design height, with a simultaneous increase in the angular availability, is achieved in accordance with an alternative embodiment of the monitoring device in accordance with the invention if the reflector includes a plurality of such individual reflectors which are arranged next to one another and e.g. each have an elongate shape. With the same angular availability, it is therefore possible to reduce the design height of the total reflector in an advantageous manner by the provision of a plurality of individual reflectors which can also be provided in the form of individual retro-reflectors.
LEDs are preferably provided as the transmission elements, with generally any kind of radiation source being able to be used. The reception element of the receiver is preferably made areally and is preferably a CCD device, a CMOS device or a PSD (=position sensitive device) device. In particular when a CCD device is used as the reception element, the transmitter is designed such that the transmission elements are operated synchronously. A pulsed operation of the transmission elements is preferably provided for the case that a PDS device is used as the reception element. Generally, the reception element can have any kind of design and be made, for example with one line or as a reception matrix.
The object underlying the invention is satisfied, on the other hand, in that electromagnet radiation is transmitted into the monitored zone by means of a group of transmission elements arranged at an end of the monitored zone and spaced apart from one another. Radiation transmitted by the transmission elements is reflected at an end of the monitored zone opposite the transmission elements such that at least a part of the group of transmission elements including a plurality of transmission elements is imaged on at least one spatially resolving reception element. A check is made as to whether a pattern formed by the imaged transmission elements on the reception elements deviates from an expected image of the transmission elements at least within pre-settable tolerance limits.
With this method, at least one optoelectronic monitoring device in accordance with the invention is preferably used.
Further preferred embodiments of the invention are also set forth in the description and the drawing.
The invention will now be described in the following by way of example with reference to the drawing.